Ghrelin is the hormone that signals us that it's time to eat. So it makes sense that there have been several attempts to create a drug to slow the release of ghrelin, to curb overeating. But most of the attempts have not, unfortunately, panned out.

In their search for a drug to curb our appetite, however, researchers may have found a way to treat, or even prevent, post-traumatic stress disorder (PTSD).

It appears that ghrelin doesn't just trigger hunger. The hormone also controls an important fear pathway in the brain thought to control our response to stress.

The ghrelin pathway seems to work independently of the classical stress pathway, and offers a whole new target for stress therapies.

Hormones usually operate by initiating a series or cascade of events, often involving other hormones and parts of the body. Ghrelin is no exception. When we are afraid of something, the amygdala, the area of the brain governing the fear response, releases growth hormone.

But what the researchers discovered is that the release of growth hormone itself seems to be under the control of ghrelin, which comes from the stomach (something to keep in mind the next time you have a nervous, uneasy feeling in the pit of it).

To test this relationship, the team exposed rats to a sudden tone. The novelty of the sound triggers a brief fear response, causing the rats to freeze in place. The researchers tested rats who were bred to overexpress growth hormone and those who were given a medication to increase the activity of ghrelin receptors.

As expected, both groups of rats froze longer in response to the startling sound than control rats — and when the researchers reversed the respective hormone receptors in the rats, their fear responses returned to normal.

Levels of both ghrelin and growth hormone increased when rats were chronically stressed, the researchers found, but the important finding was that the team discovered that the ghrelin pathway seems to work independently of the classical stress pathway, the hypothalamic-pituitary-adrenal (HPA) axis.

“That's important because it gives us a whole new target for stress therapies,” said study author Ki Goosens in a statement.

In fact, taking the results together, the researchers suggest that down the line, a preventive PTSD vaccine might be possible. “Perhaps we could give people who are going to be deployed into an active combat zone a ghrelin vaccine before they go, so they will have a lower incidence of PTSD? That's exciting because right now there's nothing given to people to prevent PTSD,” Goosens said.

PTSD is difficult to treat. It plays out in different ways in different people, and its effects can be hard to break. There are some therapies that have been promising in recent years, but it may take multiple treatment methods to help people really manage the symptoms over the course of their lives.

Study author Retsina Meyer asks, “Could you immediately reverse PTSD? Maybe not, but maybe the ghrelin could get damped down and these people could go through cognitive behavioral therapy, and over time, maybe we can reverse it.”

The study was carried out by a team at MIT, and published in the journal, Molecular Psychiatry.